McCain said that Paul and other lawmakers attacking Trump have long argued for an isolationist policy for the U.S. that would be detrimental to American interests.

"The point that they are making is that the United States should simply stay out of these areas," he said. "It's going to be a disaster.

"That's the point they make."

McCain and Paul have clashed many times in the past, including when the senior senator dubbed he and Sen. Ted Cruz of Texas "wacko birds" in 2013 for filibustering John Brennan's nomination for CIA director.

He later apologized, calling the remark "inappropriate and I apologize to them for saying that because I respect them both."